Quinacridone nanoscale pigment particles and methods of making same

ABSTRACT

A process for preparing coated nanoscale quinacridone pigment particles, includes providing a first solution containing a surface additive compound in an acid; adding a quinacridone pigment precursor or crude quinacridone pigment into the first solution and causing the surface additive compound to coat formed nanoscale quinacridone pigment particles; and adding the first solution and coated nanoscale quinacridone pigment particles into a second solution containing deionized water to form a third solution and to precipitate the coated nanoscale quinacridone pigment particles; wherein the surface additive compound is a rosin compound.

TECHNICAL FIELD

This disclosure is generally directed to nanoscale quinacridone pigmentparticles, particularly nanoscale quinacridone pigment particlescomprising a quinacridone pigment and a surface additive, and methodsfor producing such nanoscale quinacridone pigment particles. Suchparticles are useful, for example, as nanoscopic colorants for suchcompositions as inks and the like, such as ink jet ink compositions,phase change ink compositions, and non-aqueous liquid ink compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

Disclosed in commonly assigned U.S. patent application Ser. No.11/759,906 to Maria Birau et al. filed Jun. 7, 2007, is a nanoscalepigment particle composition, comprising: a quinacridone pigmentincluding at least one functional moiety, and a sterically bulkystabilizer compound including at least one functional group, wherein thefunctional moiety associates non-covalently with the functional group;and the presence of the associated stabilizer limits the extent ofparticle growth and aggregation, to afford nanoscale-sized particles.Also disclosed is a process for preparing nanoscale quinacridone pigmentparticles, comprising: preparing a first solution comprising: (a) acrude quinacridone pigment including at least one functional moiety and(b) a liquid medium; preparing a second solution comprising: (a) asterically bulky stabilizer compound having one or more functionalgroups that associate non-covalently with the functional moiety, and (b)a liquid medium; combining the first solution into the second solutionto form a third solution and effecting a reconstitution process whichforms a quinacridone pigment composition wherein the functional moietyof the pigment associates non-covalently with the functional group ofthe stabilizer and having nanoscale particle size. Still further isdisclosed a process for preparing nanoscale quinacridone pigmentparticles, comprising: preparing a first solution comprising aquinacridone pigment including at least one functional moiety in anacid; preparing a second solution comprising an organic medium and asterically bulky stabilizer compound having one or more functionalgroups that associate non-covalently with the functional moiety of thepigment; treating the second solution containing with the firstsolution; and precipitating quinacridone pigment particles from thefirst solution, wherein the functional moiety associates non-covalentlywith the functional group and the quinacridone pigment particles have ananoscale particle size.

Disclosed in commonly assigned U.S. patent application Ser. No.11/759,913 to Rina Carlini et al. filed Jun. 7, 2007, is a nanoscalepigment particle composition, comprising: an organic monoazo lakedpigment including at least one functional moiety, and a sterically bulkystabilizer compound including at least one functional group, wherein thefunctional moiety associates non-covalently with the functional group;and the presence of the associated stabilizer limits the extent ofparticle growth and aggregation, to afford nanoscale-sized pigmentparticles. Also disclosed is a process for preparing nanoscale-sizedmonoazo laked pigment particles, comprising: preparing a first reactionmixture comprising: (a) a diazonium salt including at least onefunctional moiety as a first precursor to the laked pigment and (b) aliquid medium containing diazotizing agents generated in situ fromnitrous acid derivatives; and preparing a second reaction mixturecomprising: (a) a coupling agent including at least one functionalmoiety as a second precursor to the laked pigment and (b) a stericallybulky stabilizer compound having one or more functional groups thatassociate non-covalently wit the coupling agent; and (c) a liquid mediumcombining the first reaction mixture into the second reaction mixture toform a third solution and effecting a direct coupling reaction whichforms a monoazo laked pigment composition wherein the functional moietyassociates non-covalently with the functional group and having nanoscaleparticle size. Further disclosed is a process for preparing nanoscalemonoazo laked pigment particles, comprising: providing a monoazoprecursor dye to the monoazo laked pigment that includes at least onefunctional moiety; subjecting the monoazo precursor dye to an ionexchange reaction with a cation salt in the presence of a stericallybulky stabilizer compound having one or more functional groups; andprecipitating the monoazo laked pigment as nanoscale particles, whereinthe functional moiety of the pigment associates non-covalently with thefunctional group of the stabilizer and having nanoscale particle size.

The entire disclosure of the above-mentioned applications are totallyincorporated herein by reference.

BACKGROUND

A printing ink is generally formulated according to strict performancerequirements demanded by the intended market application and requiredproperties. Whether formulated for office printing or for productionprinting, a particular ink is expected to produce images that are robustand durable under stress conditions. In a typical design of apiezoelectric ink jet printing device, the image is applied by jettingappropriately colored inks during four to six rotations (incrementalmovements) of a substrate (an image receiving member or intermediatetransfer member) with respect to the ink jetting head, i.e., there is asmall transaction of the printhead with respect to the substrate inbetween each rotation. This approach simplifies the printhead design,and the small movements ensure good droplet registration. At the jetoperating temperature, droplets of liquid ink are ejected from theprinting device and, when the ink droplets contact the surface of therecording substrate, either directly or via an intermediate heatedtransfer belt or drum, they quickly solidify to form a predeterminedpattern of solidified ink drops.

Pigments are a class of colorants useful in a variety of applicationssuch as for example paints, plastics and inks, including inkjet printinginks. Dyes have typically been the colorants of choice for inkjetprinting inks because they are readily soluble colorants and, moreimportantly, do not hinder the reliable jetting of the ink. Dyes havealso offered superior and brilliant color quality with an expansivecolor gamut for inks, when compared with conventional pigments. However,because dyes are molecularly dissolved in the ink vehicle, they areoften susceptible to unwanted interactions that lead to poor inkperformance, for example photooxidation from light (will lead to poorlightfastness), dye diffusion from the ink into paper or othersubstrates (will lead to poor image quality and showthrough), and theability for the dye to leach into another solvent that makes contactwith the image (will lead to poor water/solventfastness). In certainsituations, pigments are the better alternative as colorants for inkjetprinting inks since they are insoluble and cannot be molecularlydissolved within the ink matrix, and therefore do not experiencecolorant diffusion. Pigments can also be significantly less expensivethan dyes, and so are attractive colorants for use in all printing inks.

Key issues with using pigments for inkjet inks are their large particlesizes and wide particle size distribution, the combination of which canpose critical problems with reliable jetting of the ink (i.e. inkjetnozzles are easily blocked). Pigments are rarely obtained in the form ofsingle crystal particles, but rather as large aggregates of crystals andwith wide distribution of aggregate sizes. The color characteristics ofthe pigment aggregate can vary widely depending on the aggregate sizeand crystal morphology. Thus, an ideal colorant that is widelyapplicable in, for example, inks and toners, is one that possesses thebest properties of both dyes and pigments, namely: 1) superiorcoloristic properties (large color gamut, brilliance, hues, vividcolor); 2) color stability and durability (thermal, light, chemical andair-stable colorants); 3) minimal or no colorant migration; 4)processable colorants (easy to disperse and stabilize in a matrix); and5) inexpensive material cost. Thus, there is a need addressed byembodiments of the present invention, for smaller nanos-sized pigmentparticles that minimize or avoid the problems associated withconventional larger-sized pigment particles. There further remains aneed for processes for making and using such improved nano-sized pigmentparticles as colorant materials. The present nanosized pigment particlesare useful in, for example, paints, coatings and inks (e.g., inkjetprinting inks) and other compositions where pigments can be used such asplastics, optoelectronic imaging components, photographic components,and cosmetics among others. The following documents provide backgroundinformation:

U.S. Pat. No. 6,902,613 discloses a mixture of an organic nanosizepigment comprising of from 50 to 99% by weight of the nanosize pigmentand 1 to 50% by weight based of a low molecular weight naphthalenesulfonic acid formaldehyde polymer and its use as a particle growth andcrystal phase director for the preparation of a direct pigmentaryorganic pigment or in pigment finishing.

WO 2004/048482 discloses a mixture of an organic nanosize pigmentcomprising of from 50 to 99% by weight of the nanosize pigment and 1 to50% by weight based of a low molecular weight polysulfonatedhydrocarbon, in particular naphthalene mono- or disulfonic acidformaldehyde polymer, and its use as a particle growth and crystal phasedirector for the preparation of a direct pigmentary organic pigment orin pigment finishing.

U.S. patent application Publication No. 2006/0063873 discloses a processfor preparing nano water paint comprising the steps of: A. modifying thechemical property on the surface of nano particles by hydroxylation forforming hydroxyl groups at high density on the surface of the nanoparticles; B. forming self-assembly monolayers of low surface energycompounds on the nano particles by substituting the self-assemblymonolayers for the hydroxyl groups on the nano particles fordisintegrating the clusters of nano particles and for forming theself-assembly monolayers homogeneously on the surface of the nanoparticles; and C. blending or mixing the nano particles havingself-assembly monolayers formed thereon with organic paint to form nanowater paint.

U.S. patent applicaton Publication No. 2005/0109240 describes a methodof producing a fine particle of an organic pigment, containing the stepsof: flowing a solution of an organic pigment dissolved in an alkaline oracidic aqueous medium, through a channel which provides a laminar flow;and changing a pH of the solution in the course of the laminar flow.

U.S. Pat. No. 3,201,402 discloses a process for the production ofpigment dyestuffs of the quinacridone-7,14-dione series, which consistsof reaction 1 more of 2,5-dihalogenoterephthalic acid and one or more ofits esters either simultaneously or successively with 2 moles of anaromatic amine or of a mixture of different aromatic amines, in which atleast one position ortho to the amino group is free, and coverting theresulting 2,5-diarylaminoterephthalic acid or its ester into aquinacridone-7,14-dione by heating at a high temperature in an acidcondensation medium, if desired in presence of an inert organic solvent.

Kento Ujiiye-Ishii et al., “Mass-Production of Pigment Nanocrystals bythe Reprecipitation Method and their Encapsulation,” Molecular Crystalsand Liquid Crystals, v. 445, p. 177 (2006) describes that quinacridonenanocrystals with controlled size and morphology were readily fabricatedby using a pump as an injection apparatus of the reprecipitation methodfor mass-production and injecting concentrated N-methyl-2-pyrrolidinonesolution. The reference describes that encapsulation of quinacridonenanocrystals using polymer was achieved and quite improveddispersibility was confirmed for the encapsulated nanocrystals.

Hideki Maeta et al., “New Synthetic Method of Organic Pigment NanoParticle by Micro Reactor System,” in an abstract available on theinternet, describes a new synthetic method of an organic pigment nanoparticle was realized by micro reactor. A flowing solution of an organicpigment, which dissolved in an alkaline aqueous organic solvent, mixedwith a precipitation medium in a micro channel. Two types of microreactor can be applied efficiently on this build-up procedure withoutblockage of the channel. The clear dispersion was extremely stable andhad narrow size distribution, which were the features, difficult torealize by the conventional pulverizing method (breakdown procedure).These results proved the effectiveness of this process on micro reactorsystem.

WO 2006/132443 A1 describes a method of producing organic pigment fineparticles by allowing two or more solutions, at least one of which is anorganic pigment solution in which an organic pigment is dissolved, toflow through a microchannel, the organic pigment solution flows throughthe microchannel in a non-laminar state. Accordingly, the contact areaof solutions per unit time can be increased and the length of diffusionmixing can be shortened, and thus instantaneous mixing of solutionsbecomes possible. As a result, nanometer-scale monodisperse organicpigment fine particles can be produced in a stable manner.

K. Balakrishnan et al., “Effect of Side-Chain Substituents onSelf-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am.Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use ofcovalently-linked aliphatic side-chain substiutents that werefunctionalized onto perylene diimide molecules so as to modulate theself-assembly of molecules and generate distinct nanoparticlemorphologies (nano-belts to nano-spheres), which in turn impacted theelectronic properties of the material. The side-chain substituentsstudied were linear dodecyl chain, and a long branched nonyldecyl chain,the latter substituent leading to the more compact, sphericalnanoparticle.

WO 2006/011467 discloses a pigment, which is used, for example, in colorimage display devices and can form a blue pixel capable of providing ahigh level of bright saturation, particularly a refined pigment, whichhas bright hue and is excellent in pigment properties such aslightfastness, solvent resistance and heat resistance, and a process forproducing the same, a pigment dispersion using the pigment, and an inkfor a color filter. The pigment is a subphthalocyanine pigment that isprepared by converting subphthalocyanine of the specified formula, to apigment, has diffraction peaks at least at diffraction angles (2θ) 7.0°,12.3°, 20.4° and 23.4° in X-ray diffraction and an average particlediameter of 120 to 20 nm.

WO 2006/005536 discloses a method for producing nanoparticles, inparticular, pigment particles. Said method consists of the followingsteps: (i) a raw substance is passed into the gas phase, (ii) particlesare produced by cooling or reacting the gaseous raw substance and (iii)an electrical charge is applied to the particles during the productionof the particles in step (ii), in a device for producing nanoparticles.The disclosure further relates to a device for producing nanoparticles,comprising a supply line, which is used to transport the gas flow intothe device, a particle producing and charging area in order to produceand charge nanoparticles at essentially the same time, and an evacuationline which is used to transport the charged nanoparticles from theparticle producing and charging area.

Japanese Patent Application Publication No. JP 2005238342 A2 disclosesirradiating ultrashort pulsed laser to organic bulk crystals dispersedin poor solvents to induce ablation by nonlinear absorption for crushingthe crystals and recovering the resulting dispersions of scatteredparticles. The particles with average size approximately 10 nm areobtained without dispersants or grinding agents for contaminationprevention and are suitable for pigments, pharmaceuticals, etc.

WO 2004026967 discloses nanoparticles manufactured by dissolving organicpigments in organic solvents containing at least 50 vol. % amides andadding the organic solvent solutions in solvents, which are poorsolvents for the pigments and comparable with the organic solvents,while stirring. Thus, quinacridone pigment was dissolved in1-methyl-2-pyrrolidinone and added to water with stirring to give a fineparticle with average crystal size 20 nm.

U.S. Pat. No. 6,837,918 discloses a process and apparatus that collectspigment nanoparticles by forming a vapor of a pigment that is solid atroom temperature, the vapor of the pigment being provided in an inertgaseous carrying medium. At least some of the pigment is solidifiedwithin the gaseous stream. The gaseous stream and pigment material ismoved in a gaseous carrying environment into or through a dry mechanicalpumping system. While the particles are within the dry mechanicalpumping system or after the nanoparticles have moved through the drypumping system, the pigment material and nanoparticles are contactedwith an inert liquid collecting medium.

U.S. Pat. No. 6,537,364 discloses a process for the fine division ofpigments which comprises dissolving coarsely crystalline crude pigmentsin a solvent and precipitating them with a liquid precipitation mediumby spraying the pigment solution and the precipitation medium throughnozzles to a point of conjoint collision in a reactor chamber enclosedby a housing in a microjet reactor, a gas or an evaporating liquid beingpassed into the reactor chamber through an opening in the housing forthe purpose of maintaining a gas atmosphere in the reactor chamber, andthe resulting pigment suspension and the gas or the evaporated liquidbeing removed from the reactor through a further opening in the housingby means of overpressure on the gas entry side or underpressure on theproduct and gas exit side.

U.S. Pat. No. 5,679,138 discloses a process for making ink jet inks,comprising the steps of: (A) providing an organic pigment dispersioncontaining a pigment, a carrier for the pigment and a dispersant; (B)mixing the pigment dispersion with rigid milling media having an averageparticle size less than 100 μm; (C) introducing the mixture of step (B)into a high speed mill; (D) milling the mixture from step (C) until apigment particle size distribution is obtained wherein 90% by weight ofthe pigment particles have a size less than 100 nanometers (nm); (E)separating the milling media from the mixture milled in step (D); and(F) diluting the mixture from step (E) to obtain an ink jet link havinga pigment concentration suitable for ink jet printers.

Japanese Patent Application Publications Nos. JP 2007023168 and JP2007023169 discloses providing a pigment dispersion compound excellentin dispersibility and flowability used for the color filter which hashigh contrast and weatherability. The solution of the organic material,for example, the organic pigment, dissolved in a good solvent under theexistence of alkali soluble binder (A) which has an acidic group, and apoor solvent which makes the phase change to the solvent are mixed. Thepigment nanoparticles dispersed compound re-decentralized in the organicsolvent containing the alkali soluble binder (B) which concentrates theorganic pigment nanoparticles which formed the organic pigment as theparticles of particle size less than 1 μm, and further has the acidicgroup.

Kazuyuki Hayashi et al., “Uniformed nano-downsizing of organic pigmentsthrough core-shell structuring,” Journal of Materials Chemistry, 17(6),527-530 (2007) discloses that mechanical dry milling of organic pigmentsin the presence of mono-dispersed silica nanoparticles gave core-shellhybrid pigments with uniform size and shape reflecting those of theinorganic particles, in striking contrast to conventional milling as abreakdown process, which results in limited size reduction and wide sizedistribution.

U.S. Patent Application Publication No. 2007/0012221 describes a methodof producing an organic pigment dispersion liquid, which has the stepsof: providing an alkaline or acidic solution with an organic pigmentdissolved therein and an aqueous medium, wherein a polymerizablecompound is contained in at least one of the organic pigment solutionand the aqueous medium; mixing the organic pigment solution and theaqueous medium; and thereby forming the pigment as fine particles; thenpolymerizing the polymerizable compound to form a polymer immobile fromthe pigment fine particles.

Other publications of interest, and other aspects of which may beselected for embodiments of the present disclosure, include:

-   1) Herbst, K. Hunger, Industrial Organic Pigments, “Quinacridone    Pigments” Wiley-VCH Third Edition, p. 452-472 (2004);-   2) F. Kehrer, “Neuere Entwicklung auf den Gebiet der Chemie    organischer Pigmentfarbstoffe,” Chimia, vol. 28(4), p. 173-183    (1974);-   3) B. R. Hsieh et al, “Organic Pigment Nanoparticle Thin Film    Devices via Lewis Acid Pigment Solublization and In Situ Pigment    Dispersions,” Journal of Imaging Science and Technology, vol.    45(1), p. 37-42 (2001);-   4) Swiss Patent No. 372316 to H. Bohler et al, Nov. 30, 1963; and-   5) Swiss Patent No. 404034 to H. Bohler, Jun. 30, 1966

The appropriate components and process aspects of each of the foregoingmay be selected for the present disclosure in embodiments thereof, andthe entire disclosure of the above-mentioned references are totallyincorporated herein by reference.

SUMMARY

The present disclosure addresses these and other needs, by providingnanoscale quinacridone pigment particles and methods for producing suchnanoscale quinacridone pigment particles.

Although various processes for making quinacridone pigment particles areknown, most commercial pigments have large particle size and wide sizedistributions, which can cause problems with reliable jetting of theink. An economical procedure to overcome this is usually via saltmilling of the pigment to a smaller more uniform size. However, a needstill exists for processes to make nanoscale quinacridone pigmentparticles, in an economical and scalable manner, where the nanoscalequinacridone pigment particles can be readily dispersed as in inkvehicle.

The present disclosure provides a process to make nanoparticles ofquinacridone pigments, such as Pigment Red 122, and incorporates a classof additive to the surface of the nanopigment to enable dispersibilityinto an ink vehicle and maintain stability of the ink dispersion. Thequinacridone nanoparticles can be prepared by dissolution of theadditive and the pigment together in hot acid, such as sulfuric acid,followed by reprecipitation under high agitation in a cold aqueousmedium. This process eliminates the use of expensive solvents. Theprocess in readily scalable and cost effective, and can be easilyincorporated into a commercial manufacturing facility.

In an embodiment, the disclosure provides a process for preparing coatednanoscale quinacridone pigment particles, comprising:

-   -   providing a first solution comprising a surface additive        compound in an acid;    -   adding a quinacridone pigment precursor or crude quinacridone        pigment into the first solution and causing said surface        additive compound to coat formed nanoscale quinacridone pigment        particles; and    -   adding the first solution and coated nanoscale quinacridone        pigment particles into a second solution comprising deionized        water to form a third solution and to precipitate the coated        nanoscale quinacridone pigment particles;    -   wherein the surface additive compound comprises a rosin        compound.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present disclosure provide nanoscale quinacridonepigment particles, and methods for producing such nanoscale quinacridonepigment particles. The nanoscale quinacridone pigment particles includea rosin compound as a surface additive, which not only helps to providethe nanoscale sized particles, but also improves dispersibility andstability of the nanoscale quinacridone pigment particles in inkvehicles. In embodiments, the nanoscale quinacridone pigment particlescan be prepared by a method comprising adding the surface additive tothe concentrated acid used for the pigment dissolution, followed byaddition of the pigment. The combined pigment and additive are heatedand dissolved together to get a homogeneous coating of the surfaceadditive on the pigment surface. The pigment/additive combination isquenched together in a cold medium such as de-ionized water undervigorous agitation, to obtain a dispersed nanoparticle pigment slurry.This dispersed nanopigment slurry can be neutralized with ammoniasolution to reduce the required amount of de-ionized water washes neededto subsequently purify the isolated pigment. The wet pigment cake canthen be washed, for example with acetonitrile, to remove water to aidedrying. The pigment can also be left as a wet cake and disperseddirectly in an ink formulation.

The term “precursor” or “pigment precursor” as used in “precursor to theorganic pigment” can be any chemical substance that is an advancedintermediate in the total synthesis of a compound (such as the organicpigment). In embodiments, the organic pigment and the pigment precursormay or may not have the same functional moiety. In embodiments, thepigment precursor to the organic pigment may or may not be a coloredcompound. In still other embodiments, the pigment precursor and theorganic pigment can have different functional moieties.

Representative pigment precursors include the2,5-di-anilino-terephthalic and their corresponding ester derivativeswith any hydrocarbon chain R, as indicated in Formula 1 below. Thehydrocarbon chain R can represent (but is not limited to) hydrogen, astraight or branched alkyl group with 1 to about 20 carbons such asmethyl, ethyl, propyl, iso-propyl, butyl and the like, or cyclic alkylgroups such as cyclohexyl, or any substituted or unsubstituted arylgroup such as phenyl, naphthyl, para-methoxybenzyl, and others. Thefunctional moieties R₁ and R₂ can be present at any position on theaniline aromatic ring such as ortho, meta or para; they can be differentor identical with each other and include the following functionalgroups: H, alkyl group with 1 to about 20 carbons such as methyl, ethyl,alkoxyl group with 1 to about 20 carbons such as methoxyl, ethoxyl,aryloxyl such as phenoxyl, and arylalkoxyl such as benzyloxyl and anyhalide such as Cl, Br

Formula 1. Quinacridone Pigment Precursors

In specific embodiments, compounds of formula 1 include the following:

-   —R═H or any hydrocarbon chain, R₁═R₂═H;-   —R═H or any hydrocarbon chain, R₁═H, R₂═halide such as Cl or Br;-   —R═H or any hydrocarbon chain, R₁═R₂═CH₃, CH₂CH₃, CH₂CH₂CH₃,    CH(CH₃)₂;-   —R═H or any hydrocarbon chain, R₁═H, R₂═CH₃, CH₂CH₃, CH₂CH₂CH₃,    CH(CH₃)₂;-   —R═H or any hydrocarbon chain, R₁═CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂,    R₂═halide such as Cl or Br;-   —R═H or any hydrocarbon chain, R₁═R₂═halide such as Cl or Br;-   —R═H or any hydrocarbon chain, R₁═Cl, R₂═Br;-   —R═H or any hydrocarbon chain, R₁═R₂═O—CH₃, O—CH₂CH₃, O—CH₂CH₂CH₃,    O—CH(CH₃)₂, O—(CH₂)C₆H₅;-   —R═H or any hydrocarbon chain, R₁═H, R₂═OCH₃, O—CH₂CH₃, O—CH₂CH₂CH₃,    O—CH(CH₃)₂, O—(CH₂)C₆H₅; and-   —R═H or any hydrocarbon chain, R₁═OCH₃, O—CH₂CH₃, O—CH₂CH₂CH₃,    O—CH(CH₃)₂, O—(CH₂)C₆H₅, R₂═halide such as Cl or Br.

Representative surface additive compounds include any rosin compound,such as rosin, rosin esters, rosin acids, rosin salts, or the like, thathave the function of coating the pigment particles to limit the extentof pigment particle or molecular self-assembly so as to producepredominantly nanoscale-sized pigment particles. The rosin compounds canbe hydrogenated or not, and thus can include hydrogenated rosin,hydrogenated rosin esters, hydrogenated rosin acids, hydrogenated rosinsalts, or the like. Specific examples of such rosin compounds include,for example, hydrogenated rosin esters (such as Pinecrystal KE-100 orKE-311 manufactured by Arakawa Kagaku Co., Ltd.), hydrogenated rosinglycerin ester, levopimaric acid, neoabietic acid, palustric acid,abietic acid, dehydroabietic acid, seco-dehydroabietic acid,tetrahydroabietic acid, dihydroabietic acid, pimaric acid, andisopimaric acid, calcium resonates, zinc resonates, magnesium resonates,barium resonates, lead resonates, cobalt resonates, mixed resonates(such as calcium and zinc resonates), sodium salts of rosins (such asDRESINATE X™ from Hercules Paper Technology Group), alkyl esters ofrosin or hydrogenated rosin (such as HERCOLYN D™, a methylester ofhydrogenated rosin from Hercules, Inc., and ABALYN™, a methylester ofrosin from Hercules, Inc.), mixtures thereof, and the like. For example,one specific commercial example of a suitable surface additive compoundis KE-100, a hydrogenated rosin ester available from Arakawa ChemicalIndustries.

The surface additive coats the pigment particles to inactivate anysurface functional moieties of the pigment particle, and to limitpigment particle growth. The surface coating can, in embodiments, thecomplete such that a continuous or substantially continuous coating isprovided on the pigment particles. However, in other embodiments, thecoating can be of only a part of the pigment particles, to provide adiscontinuous coating. In either case, the coating enables not onlypigment particle growth control, but also provides surface propertiesthat enable dispersion of the formed particles into vehicles such as inkvehicles with improved dispersion and stability.

The “average” particle size, typically represented as D₅₀, is defined asthe median particle size value at the 50th percentile of the particlesize distribution, wherein 50% of the particles in the distribution aregreater than the D₅₀ particle size value and the other 50% of theparticles in the distribution are less than the D₅₀ value. Averageparticle size can be measured by methods that use light scatteringtechnology to infer particle size, such as Dynamic Light Scattering. Theterm “particle diameter” as used herein refers to the length of thecoated pigment particle as derived from images of the particlesgenerated by Transmission Electron Microscopy. The term “nanosized” (or“nanoscale” or “nanoscale sized”) such as used in “nanosized pigmentparticles” refers to, for instance, an average particle size D₅₀, ofless than about 150 nm, such as about 1 nm to about 100 nm, or about 10nm to about 80 nm. Geometric standard deviation is a dimensionlessnumber that typically estimates a population's dispersion of a givenattribute (for instance, particle size) about the median value of thepopulation and is derived from the exponentiated value of the standarddeviation of the log-transformed values. If the geometric mean (ormedian) of a set of numbers {A₁, A₂, . . . , A_(n)} is denoted as μ_(g),then the geometric standard deviation is calculated as:

$\sigma_{g} = {\exp\sqrt{\frac{\sum\limits_{i = 1}^{n}\left( {{\ln\; A_{i}} - {\ln\;\mu_{g}}} \right)^{2}}{n}}}$

Commercial pigments, having typical median particle sizes of at leastabout 100 nm to about 1 micron, have both varied particle sizedistributions and particle aspect ratios. The aspect ratio of a particlerelates its length dimension to its width dimension. Generally, theaspect ratio of a particle increases with its length dimension and,frequently, produces acicular and/or irregular morphologies that caninclude ellipsoids, rods, platelets, needles, and the like. Typically,organic pigments such as for example quinacridone pigments, have largeparticle size distribution as well as large distribution of particleaspect ratios and potentially, a large distribution of particlemorphologies. This scenario is undesirable, as it can lead tonon-dispersed, phase-segregated inks or dispersions and the like madefrom such pigments having a large distribution of particle size and/oraspect ratio.

Quinacridone nanopigments, when properly synthesized using exemplaryconditions and surface additives outlined herein in embodiments, willhave a more regular distribution of particle sizes and particle aspectratio (length:width), the latter being about less than 4:1 with themedian particle size being less than about 100 nm, as determined using adynamic light scattering technique such as with a particle sizeanalyzer.

An advantage of the processes and compositions of the disclosure is thatthey provide the ability to tune particle size and composition for theintended end use application of the quinacridone pigment. This leads toan overall higher color purity of the pigment particles when they aredispersed onto various media for being coated, sprayed, jetted,extruded, etc.

There are several known methods for the total synthesis of quinacridonepigments, which consist of chemical transformations to form thepentacyclic ring system by either the thermally-induced ring closure orthe acid-catalyzed ring closure as described by W. Herbst and K. Hungerin Industrial Organic Pigments, chapter “Quinacridone Pigments”Wiley-VCH Third Edition, p. 452-472 (2004). The pentacyclic ring systemof quinacridone can be approached by the latter acid-catalyzed ringclosure reaction on a 2,5-dianilino terephthalic acid or ester pigmentprecursor, as illustrated in Formula (1) above and the followingreaction schemes, which in turn is prepared from one of two knownstarting materials: a) succinate esters, and b) 2,5-dihalo-terephthalicacid.

In embodiments, surface additive coated nano-sized particles ofquinacridone pigment can be prepared in one of two ways: 1) solubilizingcrude quinacridone pigment into an acidic liquid (commonly known as“acid pasting”) and reprecipitation of the pigment as nanoparticlesunder certain conditions; and 2) synthesis of nano-sized particles ofquinacridone pigment by acid-catalyzed ring closure of an advancedpigment precursor.

In embodiments, the surface additive is added to the acid medium beforethe pigment or pigment precursor materials. Thus, the surface additiveis solubilized or dispersed in the acid medium, such as by stirring orthe like. The acid medium can be heated to or maintained at a desiredtemperature, such as from about 0° C. to about 100° C., such as about20° C. to about 80° C. or about 40° C. to about 60° C. However, inembodiments, the acid medium is heated to a temperature above roomtemperature, as a higher temperature assists in the dissolution of thesurface additive as well as the subsequent dissolution of the pigmentmaterials.

In these methods, a first solution is prepared or provided thatcomprises the surface additive dissolved or dispersed in a strong acid.The strong acid can be, for example, a mineral acid, an organic acid, ora mixture thereof. Examples of strong mineral acids include sulfuricacid, nitric acid, perchloric acid, various hydrohalic acids (such ashydrochloric acid, hydrobromic acid, and hydrofluoric acid),fluorsulfonic acid, chlorosulfonic acid, phosphoric acid, polyphosphoricacid, boric acid, mixtures thereof, and the like. Examples of strongorganic acids include organic sulfonic acid, such as methanesulfonicacid and toluenesulfonic acid, acetic acid, trifluoroacetic acid,chloroacetic acid, cyanoacetic acid, mixtures thereof, and the like

This first solution can include the strong acid in any desirable amountor concentration, such as to allow for desired dissolution or dispersionof the surface additive and the subsequent dissolution or dispersion ofthe pigment particles. The amount of acid solution can be selected suchthat after pigment addition, the acid solution contains pigment in aconcentration of 0.5% to 20%, such as 1% to 15% or 2% to 10% by weight,although the values can also be outside these ranges.

In the method 1), the crude quinacridone pigment is added to the strongacid solution of surface additive. The addition is generally conductedslowly, such as dropwise, with vigorous agitation, although the additioncan be conducted in various other ways. The addition can also beconducted with a minor amount of a surface-active agent or other commonadditive, if desired. During the addition, the temperature is maintainedanywhere in the above temperature ranges, although the re-precipitationof quinacridone pigment to form nanoparticles can be held isothermallywithin or outside this temperature range, in one embodiment and, inanother embodiment, the temperature during re-precipitation ofquinacridone pigment to form nanoparticles can also be allowed to cycleup and down within or outside this temperature range.

Once the pigment material is added to the first solution, the firstsolution can be held and stirred for an amount of time to allow suitableand desired coating of the pigment particles by the surface additive.This process can be allowed to take place, for example, for a period oftime of about 10 minutes to about 10 hours, such as about 1 to about 5hours or about 2 to about 4 hours, as desired.

Any suitable liquid medium can be used to carry out the re-precipitationof the quinacridone pigment so as to afford surface additive coatednano-sized particles. Desirably, the re-precipitation can be carried outin deionized water, which avoids the use of costly organic solvents andthe additional washing and separation steps needed in the pigmentparticle recovery. The second solution, in which the re-precipitation iscarried out, thus desirably includes deionized water as the majorcomponent.

If desired, a precipitating agent can also be incorporated into thesecond solution. Any liquid that will not dissolve the coated pigmentcan be used as an optional precipitating agent. Suitable precipitatingagents include, but are not limited to, alcohols such as methanol,ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol; water,tetrahydrofuran, ethyl acetate, hydrocarbon solvents such as hexanes,toluene, xylenes, Isopar solvents, and mixtures thereof. The optionalprecipitating agent can also be ammonia solution (concentrated solutionor other percentages). The precipitating agent can be added in a rangeof about 10% to about 100% by volume of the total volume of the mixture,such as between about 20% and about 80%, or between about 30% and about70%.

The re-precipitation of the pigment to form nano-sized particles can beconducted by adding the first solution of dissolved pigment and surfaceadditive to the second (re-precipitation) solution. In embodiments, thisaddition is conducted slowly by adding the first solution to the secondsolution under vigorous agitation such as by use of high-speedmechanical stirring or homogenization or other means.

In this method 1), the re-precipitation process can be conducted at anydesired temperature to allow for formation of coated quinacridonenanoparticles while maintaining solubility of the first and secondsolutions. For example, the re-precipitation can be conducted at atemperature of from about 0° to about 90° C., such as from about 0° toabout 40° C., or from about 0° to about 20° C., although temperaturesoutside of these ranges can be used, if desired. In one embodiment, there-precipitation can be performed essentially isothermally, where asubstantially constant temperature is maintained, while in anotherembodiment, the temperature during re-precipitation can be allowed tofluctuate within a desired range, where the fluctuation can be cyclic orthe like.

Once the re-precipitation is complete, the quenched mixture can beneutralized (to neutralize the acid) by adding a suitable base to thesolution. For example, the solution can be neutralized by the dropwiseaddition of aqueous ammonia solution. Other suitable neutralizing agentscan include alkali metal hydroxides and carbonates, such as NaOH, KOH,Na₂CO₃, K₂CO₃, and the like.

Once the neutralization is complete, the pigment nanoparticles can beseparated from the solution by any conventional means, such as forexample, vacuum-filtration methods or centrifugal separation methods.The nanoparticles can also be processed for subsequent use according toknown methods.

Due to the nature of the small size of the nanoparticles that are formedfrom this process, the pigment can form a foam in solution, which isvery difficult to filter. To help overcome the foam and aide thefilter/pigment isolation procedure, a de-foaming agent can added to theneutralized solution. Any suitable d-foaming agent can be used, and anexample includes 2-ethylhexyl alcohol, which can be used in an amount ofabout 2 to about 20 weight percent of the pigment loading. Otherde-foaming agents can also be used.

A second method of making surface additive coated nano-sized particlesof quinacridone pigment involves acid-catalyzed ring closure of aquinacridone pigment precursor. In this second method 2), the pigment issynthesized concurrently with nanoparticle formation. That is, pigmentmolecules are prepared from precursor compounds according to knownchemical synthesis processes, except that within a key step thatinvolved acid-catalyzed ring closure to form the quinacridonepentacyclic ring system, the above-described surface additive compoundis introduced, to coat the formed nanopigment particles.

Various processes for synthesizing quinacridone pigments are well knownin the art. For example, U.S. Pat. Nos. 2,821,529 and 2,821,541 eachdescribe a six-step process for making quinacridone pigments byconstructing the middle aromatic ring first. A newer approach, describedby Von F. Kehrer, Chimia, vol. 26, p. 173 (1974), is a three-stepprocess beginning from an aromatic starting material. The entiredisclosures of these references are incorporated herein by reference.For example, various pigment precursors of formula (1) above can beproduced from aromatic starting materials, and then subsequently thesepigment precursors are subjected to an acid-catalyzed ring closurereaction. If this reaction is performed in the presence of the describedsurface additives, the desired coated quinacridone pigment nanoparticlesare formed.

For example, one embodiment of the second method discloses the synthesisof quinacridone pigment nanoparticles starting from a halogenatedaromatic raw material, as outlined in scheme (1) above. A keyintermediate is the pigment precursor, 2,5-dianilino terephthalic acidor its diester derivative, as illustrated in Formula (1). Anacid-catalyzed cyclization is performed on this pigment precursor in thepresence of the surface additive compound. In this particular method,the acid-catalyzed cyclization can be conducted in any suitable acidicliquid medium, such as, for example, in the presence of any of thestrong acids as described previously for the first method of makingquinacridone pigment nanoparticles. Representative examples include, butare not limited to, sulfuric acid, nitric acid, mono-, di-, and tri-haloacetic acids such as trifluoroacetic acid, dichloroacetic acid and thelike, halogen acids such as hydrochloric acid, phosphoric acid andpolyphosphoric acid, boric acid, and a variety of mixtures thereof. Asin the first method above, the first solution in which theacid-catalyzed cyclization occurs already has the surface additivesolublizied or dispersed therein.

During the acid-catalyzed cyclization reaction, the presence of theadded surface additive coats the nanoparticles as they are formed, tothereby control and limit particle growth. In this way, the pigmentparticle size and morphology can be controlled and even tailored byproviding surface additive compositions and process conditions thatlimit pigment particle growth to a desired level.

The re-precipitation and neutralization in the second method can beconducted in the same manner as in the first method. Once there-precipitation and neutralization is complete, the coated pigmentnanoparticles can be separated from the solution by any conventionalmeans, such as for example, vacuum-filtration methods or centrifugalseparation methods. The nanoparticles can also be processed forsubsequent use according to known methods.

Each of the methods allows for narrow control of the pigment particlesize and morphology, and particle size and morphology distribution. Forexample, these methods allow for controlling the pigment particle sizeto be of nanoscale size, having an average particle size of less thanabout 150 nm, such as ranging from about 10 nm to about 100 nm, or about10 nm to about 80 nm, and with a narrow particle size distribution(GSD), such as about 1.1 to about 1.8, such as about 1.2 to about 1.7,or about 1.3 to about 1.5. Likewise, the formed nanopigments can have anarrow aspect ratio range of, for example, less than about 4:1(length:width).

The formed nanoscale quinacridone pigment particles can be used, forexample, as colorants in a variety of compositions, such as in liquid(aqueous or non-aqueous) ink vehicles, including inks used inconventional pens, markers, and the like, liquid ink jet inkcompositions, solid or phase change ink compositions, and the like. Forexample, the colored nanoparticles can be formulated into a variety ofink vehicles, including solid inks with melt temperatures of about 60 toabout 140° C., solvent-based liquid inks or radiation and UV-curableliquid inks comprised of alkyloxylated monomers, and even aqueous inks.

The invention will now be described in detail with respect to specificexemplary embodiments thereof, it being understood that these examplesare intended to be illustrative only and the invention is not intendedto be limited to the materials, conditions, or process parametersrecited herein. All percentages and parts are by weight unless otherwiseindicated.

EXAMPLES Example 1

In a 2 L jacketed reactor vessel fitted with a mechanical agitator(Heidolph mixer), condenser, and temperature probe, 750 g ofconcentrated (96-98%) sulfuric acid. The agitator is started and set to300 rpm. 1.5 g (3 wt %) of KE-100 Pine Crystal (from Arakawa ChemicalIndustries) is added to the acid. 50 g of PR122 (from Dainichiseika) isadded to the stirred acid mixture over a period of 30 minutes. Anitrogen atmosphere is introduced into the reactor and the mixture isheated to 50° C. in 30 minutes, using a ciruclatory bath attached to thereactor jacket, and kept at 50° C. for 3 hours to fully dissolve thepigment.

In a 6 L jacketed reactor vessel fitted with a mechanical agitator (IKAmixer) with a P4 stirrer blade, condenser with nitrogen fitting andtemperature probe is charged 1200 g de-ionized water. The reactoragitator is started and adjusted to 420 rpm. Cooling is applied to the 6L reactor with a circulatory bath to bring the de-ionized watertemperature to 5° C. After the 3 hour pigment dissolution time in the 2L reactor, the pigment solution is added to the chilled and stirredde-ionized water dropwise over a period of 90 minutes, to quench theacid and precipitate the pigment. The reaction mixture is maintained at5-10° C. during the quenching step via cooling applied to the reactorjacket via the circulatory bath. The quenched mixture is neutralized bythe dropwise addition of 1000 g of 26-30% aqueous ammonia solution overa period of 90 minutes. The reaction mixture is maintained at 5-15° C.during the neutralization step via cooling applied to the reactor jacketvia the circulatory bath. The pigment is filtered and concentrated usinga Crossflow filtration unit fitted with a 0.5 micron ceramic filterelement. The concentrated pigment slurry undergoes repeatedwashing/concentration with fresh de-ionized water, using the Crossflowunit, until the filtrate pH is 8. The concentrated pigment slurry isthen vacuum filtered in a Nutche type filter (fitted with a 0.5 μ Gortexfilter media) to isolate a wet pigment cake. The wet pigment cake isthen re-slurry washed (in a beaker and magnetic stir bar) with freshdeionized water and filtered in the Nutche filter. This repeatedwashing/filtration is repeated until the wash filtrate is pH 7 andconductivity less than 100 μS/cm. The pigment undergoes a finalacetonitrile re-slurry wash and filtration to remove water. The isolatedcake is dried in a vacuum tray dryer under vacuum at 50° C. until dry.The dried pigment is de-lumped in a coffee grinder, to yield ˜35 gpigment.

A dispersion of the pigment made in Example 1 above dispersed in thefollowing manner. To a 30 mL bottle were added 70.0 g of ⅛ inch diameter440 C Grade 25 steel balls (available from Hoover Precision Products,Inc.) and then a solution of 0.297 g OLOA 11000 (available from ChevronOronite Company LLC) in 6.28 g Isopar V (available from Alfa ChemicalsLtd.). To this were added 0.132 g of the pigment, from Example 1 above,at which point the bottle was placed on a jar mill with the speedadjusted such that the bottle was rotating at about 7 cm/s for 4 days.After the dispersion had been ball-milled for 4 days, 1 g of theresultant dispersion was transferred to a 1 dram vial and allowed toremain in an oven at 120° C. where the dispersion's viscosity andthermal stability were qualitatively assessed. The low-to-mediumviscosity dispersion showed excellent stability at 120° C. where nosettling of pigment particles from the vehicle was observed over 9 days(and only slight settling was observed after being held for 3 weeks at120° C.) indicating excellent thermal stability characteristics aboutthe dispersion.

COMPARATIVE EXAMPLE 1

In a 2 L jacketed reactor vessel fitted with a mechanical agitator(Heidolph mixer), condenser, and temperature probe, 750 g ofconcentrated (96-98%) sulfuric acid. The agitator is started and set to300 rpm. 50 g of PR122 (from Dainichiseika) is added to the stirred acidmixture over a period of 30 minutes. A nitrogen atmosphere is introducedinto the reactor and the mixture is heated to 50° C. in 30 minutes,using a circulatory bath attached to the reactor jacket, and kept at 50°C. for 3 hours to fully dissolve the pigment.

In a 6 L jacketed reactor vessel fitted with a mechanical agitator (IKAmixer) with a P4 stirrer blade, condenser with nitrogen fitting andtemperature probe is charged 200 g de-ionized water. The reactoragitator is started and adjusted to 420 rpm. Cooling is applied to the 6L reactor with a circulatory bath to bring the de-ionized watertemperature to 5° C. After the 3 hour pigment dissolution time in the 2L reactor, the pigment solution is added to the chilled and stirredde-ionized water dropwise over a period of 90 minutes, to quench theacid and precipitate the pigment. The reaction mixture is maintain at5-10° C. during the quenching step via cooling applied to the reactorjacket via the circulatory bath. The pigment is filtered andconcentrated using a Crossflow filtration unit fitted with a 0.5 micronceramic filter element. The concentrated pigment slurry undergoesrepeated washing/concentration with fresh de-ionized water, using theCrossflow unit, until the filtrate pH is 1.5-2.0. The concentratedpigment slurry is then vacuum filtered in a Nutche type filter (fittedwith a 0.5 μ Gortex filter media) to isolate a wet pigment cake. The wetpigment cake is then re-slurry washed (in a beaker and magnetic stirbar) with fresh de-ionized water and filtered in the Nutche filter. Thisrepeated washing/filtration is repeated until the wash filtrate is pH 6and conductivity less than 100 μS/cm. The isolated cake is dried in avacuum tray dryer under vacuum at 50° C. until dry. The dried pigment isde-lumped in a coffee grinder, to yield 39 g pigment.

A dispersion of the pigment made above (comparative example 1) wasdispersed in the following manner. To a 30 mL bottle were added 70.0 gof ⅛ inch diameter 440C Grade 25 steel balls (available from HooverPrecision Products, Inc.) and then a solution of 0.297 g OLOA 11000(available from Chevron Oronite Company LLC) in 6.28 g Isopar V(available from Alfa Chemicals Ltd.). To this were added 0.132 g of thepigment, made as above, at which point the bottle was placed on a jarmill with the speed adjusted such that the bottle was rotating at about7 cm/s for 4 days. After the dispersion had been ball-milled for 4 days,1 g of the resultant dispersion was transferred to a 1 dram vial andallowed to remain in an oven at 120° C. where the dispersion's viscosityand thermal stability were qualitatively assessed. The low viscositydispersion showed extreme settling of particles after only 1 day at 120°C. indicating extremely poor thermal stability characteristics about thedispersion.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A process for preparing coated nanoscale quinacridone pigmentparticles, comprising: providing a first solution comprising a surfaceadditive compound in an acid; adding a quinacridone pigment precursor orcrude quinacridone pigment into the first solution and causing saidsurface additive compound to coat formed nanoscale quinacridone pigmentparticles; and adding the first solution and coated nanoscalequinacridone pigment particles into a second solution comprisingdeionized water to form a third solution and to precipitate the coatednanoscale quinacridone pigment particles; wherein the surface additivecompound comprises a rosin compound.
 2. The process of claim 1, furthercomprising heating the quinacridone pigment precursor or crudequinacridone pigment, and surface additive compound, in said firstsolution.
 3. The process of claim 1, further comprising neutralizing thethird solution by adding a neutralizing agent.
 4. The process of claim3, wherein the neutralizing agent is selected from the group consistingof an ammonia solution, alkali metal hydroxides, and alkali metalcarbonates.
 5. The process of claim 1, wherein the coated nanoscalequinacridone pigment particles have any average particle diameter ofless than about 150 nm as derived from Transmission Electron Microscopy.6. The process of claim 1, wherein the nanoscale quinacridone pigmentparticles are formed from a quinacridone precursor selected from thegroup consisting of 2,5-dianilino terephthalic acid derivatives,compounds of Formula 1 and esters and amides thereof that possesslinear, branched or cyclic alkyl groups having from 1 to about 20 carbonatoms

wherein R represents hydrogen, a linear, branched or cyclic alkyl grouphaving from 1 to about 20 carbon atoms, or substituted or unsubstitutedaryl groups; R₁ and R₂ each independently represents H, alkyl, alkoxyl,and aryloxyl groups, and halogen atoms.
 7. The process of claim 1,wherein the nanoscale quinacridone pigment particles are formed from aquinacridone precursor selected from the group consisting of compoundsof the following Formula (1):

wherein R represents hydrogen, a linear, branched or cyclic alkyl grouphaving from 1 to about 20 carbon atoms or substituted or unsubstitutedaryl groups; R₁ and R₂ each independently represents H, alkyl, alkoxyl,and aryloxyl groups, and halogen atoms.
 8. The process of claim 7,wherein the nanoscale quinacridone pigment particles are formed from aquinacridone precursor selected from the group consisting of: a)compound of the formula (1) wherein R₁═R₂═H; b) compound of the formula(1) wherein R₁═H, R₂═halide; c) compound of the formula (1) whereinR₁═R₂═CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂; d) compound of the formula (1)wherein R₁═H, R₂═CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂; e) compound of theformula (1) wherein R₁═CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂; R₂═halide; f)compound of the formula (1) wherein R₁═R₂═halide; g) compound of theformula (1) wherein R₁═Cl, R₂═Br; h) compound of the formula (1) whereinR₁═R₂═OCH₃, O—CH₂CH₃, O—CH₂CH₂CH₃, O—CH(CH₃)₂, O—(CH₂)C₆H₅; i) compoundof the formula (1) wherein R₁═H, R₂═OCH₃, O—CH₂CH₃, O—CH₂CH₂CH₃,O—CH(CH₃)₂, O—(CH₂)C₆H₅ and j) compound of the formula (1) whereinR₁═OCH₃, O—CH₂CH₃, O—CH₂CH₃, O—CH₂CH₂CH₃, O—CH(CH₃)₂, O—(CH₂)C₆H₅,R₂═halide.
 9. The process of claim 1, wherein the rosin compound isselected from the group consisting of hydrogenated and non-hydrogenatedforms of rosins, rosin esters, rosin acids, rosin salts, and mixturesthereof.
 10. The process of claim 1, wherein the rosin compound isselected from the group consisting of hydrogenated rosin glycerin ester,levopimaric acid, neoabietic acid, palustric acid, abietic acid,dehydroabietic acid, seco-dehydroabietic acid, tetrahydroabietic acid,dihydroabietic acid, pimaric acid, and isopimaric acid, calciumresonates, zinc resonates, magnesium resonates, barium resonates, leadresonates, cobalt resonates, mixed resonates, sodium salts of rosins,alkyl esters of rosin or hydrogenated rosin, and mixtures thereof. 11.The process of claim 1, wherein the surface additive compound forms acontinuous or substantially continuous coating on said nanoscalequinacridone pigment particles.
 12. The process of claim 1, wherein thesurface additive compound improves dispersibility and stability of thenanoscale quinacridone pigment particles in an ink vehicle.
 13. Theprocess of claim 1, comprising adding crude quinacridone pigment to saidfirst solution.
 14. The process of claim 1, wherein the acid is selectedfrom the group consisting of strong mineral acids and strong organicacids.
 15. The process of claim 14, wherein the acid is selected fromthe group consisting of sulfuric acid, nitric acid, perchloric acid,hydrohalic acids, fluorosulfonic acid, chlorosulfonic acid, phosphoricacid and polyphosphoric acid, boric acid, organo-sulfonic acid,arenesulfonic acids, acetic acid, haloacetic, dihaloacetic,trihaloacetic acids, cyanoacetic acid, and mixtures thereof.
 16. Theprocess of claim 1, further comprising adding a precipitating agent toat least one of the second and third solutions.
 17. The process of claim1, wherein the precipitating is conducted at a temperature of from abot0 to about 90° C.
 18. The process of claim 1, comprising addingquinacridone pigment precursor to said first solution.
 19. The processof claim 18, wherein the adding quinacridone pigment precursor to saidfirst solution further comprises a chemical transformation to formquinacridone pigment molecules from said quinacridone pigment precursor.20. The process of claim 1, wherein a concentration of the coatednanoscale quinacridone pigment particles present in the third solutionis from about 0.5% to about 20% by weight.